feat: add show/hide chat panel with Ctrl+B shortcut

- Add toggle button in chat panel header
- Implement collapsed state with thin vertical strip
- Add Ctrl+B keyboard shortcut to toggle visibility
- Canvas expands to full width when chat is hidden
- Smooth 300ms transition animation

app/page.tsx

@@ -7,6 +7,7 @@ import { useDiagram } from "@/contexts/diagram-context";
 export default function Home() {
     const { drawioRef, handleDiagramExport } = useDiagram();
     const [isMobile, setIsMobile] = useState(false);
+    const [isChatVisible, setIsChatVisible] = useState(true);
 
     useEffect(() => {
         const checkMobile = () => {
@@ -23,6 +24,22 @@ export default function Home() {
         return () => window.removeEventListener("resize", checkMobile);
     }, []);
 
+    // Add keyboard shortcut for toggling chat panel (Ctrl+B)
+    useEffect(() => {
+        const handleKeyDown = (event: KeyboardEvent) => {
+            if ((event.ctrlKey || event.metaKey) && event.key === 'b') {
+                event.preventDefault();
+                setIsChatVisible((prev) => !prev);
+            }
+        };
+
+        window.addEventListener('keydown', handleKeyDown);
+
+        return () => {
+            window.removeEventListener('keydown', handleKeyDown);
+        };
+    }, []);
+
     if (isMobile) {
         return (
             <div className="flex items-center justify-center h-screen bg-gray-100">
@@ -37,7 +54,7 @@ export default function Home() {
 
     return (
         <div className="flex h-screen bg-gray-100">
-            <div className="w-2/3 p-1 h-full relative">
+            <div className={`${isChatVisible ? 'w-2/3' : 'w-full'} p-1 h-full relative transition-all duration-300 ease-in-out`}>
                 <DrawIoEmbed
                     ref={drawioRef}
                     onExport={handleDiagramExport}
@@ -49,8 +66,11 @@ export default function Home() {
                     }}
                 />
             </div>
-            <div className="w-1/3 h-full p-1">
-                <ChatPanel />
+            <div className={`${isChatVisible ? 'w-1/3' : 'w-12'} h-full p-1 transition-all duration-300 ease-in-out`}>
+                <ChatPanel
+                    isVisible={isChatVisible}
+                    onToggleVisibility={() => setIsChatVisible(!isChatVisible)}
+                />
             </div>
         </div>
     );